The field of this invention is the design of bats for baseball or softball to improve their ball-hitting effectiveness. More particularly, this invention is concerned with the construction of tubular baseball bats to provide an optimized power zone.
Historically baseball bats have been formed from solid wood. White ash bats have been preferred for use in professional baseball. In recent years, bats formed from tubular aluminum have been accepted for use in competitive amateur baseball. Such aluminum bats are widely used in Little League, high school, and college for playing softball, and also to a lesser extent for baseball.
Aluminum bats have the advantage over wooden bats of being stronger and much less subject to breakage. Further, aluminum bats have been shown to provide a somewhat larger sweet spot than corresponding wooden bats. See Bryant, et al. Research Quarterly (1977) 48: 505-510; and Brancazio, SPORTSCIENCE, 1984, pages 234-241 (Simon & Schuster, N.Y.).
The term "sweet spot" refers to the area on the barrel of the bat at which the collision with the ball feels smooth, effortless, and true. As described by Brancazio (cited above), the sweet spot is believed to correspond with the "center of percussion," which is defined in mechanics for a rotating object as the point at which an applied impulse creates no reaction at the pivot point.
The tests reported by Bryant et al. (cited above) indicated that the center of percussion of a wooden bat is substantially confined to a very narrow point or zone. With hollow aluminum bats, the tests appeared to indicate that the sweet spot extended over a wide area of perhaps 1-2 inches. Bryant et al. suggested that the enlarged sweet spot may result from the peripheral distribution of the bat weight.
Prior patents relating to tubular metal bats have disclosed a variety of means for improving bat performance. In particular, various means have been disclosed for adding weight to the barrel end portions of the bats. (See, for example, U.S. Pat. Nos. 1,499,128, 3,116,926, and 3,963,239.) Other means for improving the performance of foam-filled tubular metal bats are described in U.S. Pat. Nos. 3,801,098 and 3,972,528. None of these patents, however, relates specifically to means for enlarging the sweet spot or center of percussion of the bats or for changing its location.
A primary disadvantage of weighting a tubular metal bat at its barrel end is the resulting increase in swing resistance. The amount of effort required to swing the bat at a given velocity is appreciably increased by barrel end weighting. Consequently, since the velocity of the hit ball and the distance it travels are directly related to the mass and velocity of the bat at the point of impact, adding weight to the barrel end of the bat can result in reduced hitting power for the batter.
Brancazio (cited above), at page 234, points out the impact velocity cannot in practice be maximized hitting the ball at the extreme outer end of the bat. In this connection, the reference states that "when the ball is hit at the very end of the bat, the ball does not seem to travel as far, and contact also produces a stinging sensation in the hands." This is because the sweet spot or center of percussion is located inwardly from the barrel end. While the exact center of percussion depends on the location of the pivot point, the extent of pivot point movement is not usually very great. As summarized by Brancazio (page 237): "For most baseball bats held in the conventional way, the center of percussion is located about 6 to 8 inches from the fat end of the bat."
An early patent relating to solid wooden bats proposed weighting of the knob end of the bat (U.S. Pat. No. 1,026,990 of 1912). The purpose of the added weight was "to counteract the shock due to the impact and to preserve the equipoise of the bat" (col. 1, lines 10-12). The patent does not describe any other benefit, and, as far as is known, weighted end caps or knobs have not been applied to hollow metal bats.